In the field of manufacturing a variety of electronic devices represented by a semiconductor device, fine processing technology in a half-micron level is requisite for completely meeting the requirements of further densification and integration of the device itself. Among others, requirements for photolithography usable for forming a fine pattern to allow for such fine processing has increasingly become more exacting. Specifically, in the case of manufacturing a DRAM with an integration degree of 1 G bits or higher, processing technology with a minimum line width of 0.13 μm or less is needed therefor. For complying with such rules, there has been employed photolithography using ArF excimer laser (193 nm) as exposure light. For the purpose of processing a further finer pattern, development in photolithography technology using F2 excimer laser (157 nm) as exposure light has progressed recently [R. R. Kunz et al., Journal of Vacuum Science and Technology, Vol. B17(6), pp.3267–3272 (1999)].
Accordingly, there have been made, in parallel, progress in the development of resist materials adaptable to such photolithography using F2 excimer laser (157 nm) as exposure light. As to performance required for a resist material fit to F2 excimer laser exposure, in addition to a higher resolving potential answering such increased fineness in processing size, demand for higher sensitivity is on the rise. Specifically since a laser apparatus itself is expensive and a gas used as a laser medium has a short life in terms of F2 excimer laser used for exposure, it is desired that a more sensitive resist material is used to minimize the quantity of exposure light required for each patterning process and thus to improve cost performance of the laser.
It is well known that a chemical-amplification-type resist with use of a photo-acid generator operating as a photo-sensitizer is one of hopeful approach for making a resist material more sensitive. Such approach as chemical-amplification-type resists have been also extensively used for a conventional resist material for KrF excimer laser exposure [e.g., Hiroshi Ito, C. Grant Wilson, American Chemical Society Symposium series, Vol, 242, pp.11–23 (1984)]. For example, in JP 2-27660 A1, disclosed is a chemical-amplification-type resist for which triphenylsulfonium hexafluoroarsenate is used as a photo-acid generator in combination with (p-tert-butoxycarbonyloxy-α-methylstyrene) as a resist resin. A characteristic feature of such chemical-amplification-type resist is that chemical amplification is achieved due to multiple acceleration of reaction in such a way that the photo-acid generator added as a photosensitizer component generates a proton acid in response to exposure light irradiation; and when heat-treating the resist post to the exposure step, one molecule of the proton acid generated by absorption of one photon induces and catalyzes an acid catalytic reactions of a resist resin or the like. A chemical-amplification-type resist utilizes said mechanism to realize drastically higher sensitivity in comparison with a conventional resist with a photoreaction efficiency (reaction per one photon) of less than 1. Currently, majority of resist materials being under development for excimer laser exposure belong to a chemical-amplification-type.